mechanical temp gauge location

No the stat transfers above the spacer. I am not personally "excited" about the accuracy of a sender in the drain plug

I would not remove the intake, just drain some coolant and drill and tap. You will NEED however, to get some practice if you are not familiar, and be CAREFUL tapping an aluminum intake as they will be somewhat thin there. And don't drive the tap in very deep as they are tapered. Be careful not to use an oversize drill and tap a little and try it etc "if you do"